We’re experiencing an issue with call forwarding when initiating a call from a real device (using a physical SIM card). The AI agent is configured to forward the call to a valid US number. However, every time the call is forwarded, it results in a “Busy” signal, even though the receiver is available and can receive calls normally. Details: • When the same forwarding logic is used with a Twilio or Plivo number as the caller, the call connects successfully and the forwarding works as expected. • The issue only occurs when the original call is initiated from a real device (SIM-based), not from a virtual number. • The forwarding number is a valid, reachable US phone number. • There is no indication of network issues or Do Not Disturb mode on the recipient’s device. • We suspect there may be a compatibility or signaling issue when forwarding calls originating from carrier-based numbers. Steps to Reproduce: 1. Use a real device with a SIM to initiate a call to our system. 2. The AI agent answers and attempts to forward the call to a US number. 3. The call immediately fails with a “Busy” signal. 4. Repeat the same flow with a Twilio/Plivo number – the call successfully connects and forwards. Provider : twilio

Suggestion: Check Twilio's call logs for SIP signaling errors when forwarding calls from a real device, as there may be compatibility issues with how carrier-based calls are handled. Try switching the transfer mode in your Vapi configuration to "warm-transfer-with-twiml" or "SIP REFER" to see if the issue persists. If the problem continues, contact Twilio support with call SIDs and logs for deeper signaling analysis. For more details on transfer modes and troubleshooting, see the [Vapi call forwarding documentation](https://docs.vapi.ai/call-forwarding). Source: - [Call Forwarding Vapi Documentation](https://docs.vapi.ai/call-forwarding)

Message marked as helpful by @jetani_ravi! 🎉

Hey! To help track down this issue, could you share: - The call ID This would really help us figure out what went wrong!